Generally, solids in slurry suspensions are filtered, and the solids are subsequently slurried again (hereinafter also referred to as reslurried), dissolved or dispersed again in a solvent for cleaning or dissolving or for other purposes. In such a case, the slurry suspensions are generally discharged outside a vessel temporarily in widely adopted methods, which include a method comprising the steps of subjecting the slurry suspensions to solid-liquid separation using a continuous or batch-type filtering device installed outside the vessel, transferring the separated solids to another vessel, and introducing a solvent to the solids to reslurry, dissolve or disperse the same; or a method comprising the step of performing filtration and reslurrying (optionally further performing dissolution or dispersion) using a batch-type filtering device installed outside the vessel. For example, Japanese Patent Laid-Open No. 2000-219706 also discloses a method comprising the steps of temporarily discharging a slurried polymer obtained by the treatment after polymerization, separating the polymer by filtration, then washing it with water in a separate container, obtaining a polymer by filtration, transferring the polymer to another container, and finally redispersing the polymer in water. Moreover, a horizontal filter press as shown below, in which filtration, reslurrying, cleaning, and dissolution or dispersion are performed, is widely adopted:    “SN-type automatic cake-scraping filter press” made by Japan Chemical Engineering & Machinery Co., Ltd.    “Multifunctional filter press” made by NGK Insulators, Ltd.These filtering devices are generally equipped with filter cloths, filter net or filter plates each having openings, and in the case of a continuous filtering device, since it continuously uses such a filter medium, it has an advantage of reducing the size of the device itself. However, there are various problems in continuous filtering devices. For example, many driving parts are required, thereby increasing the parts requiring frequent maintenance; device cost essentially tends to be high; and since the device itself is of an open-type, use of any solvent may adversely affect environment.
On the other hand, in the case of a batch-type filtering device, since the amount that can be treated in one operation is limited, when the amount of treatment is intended to be increased, the size of the device itself tends to be increased. Moreover, numbers of filtering devices, both of continuous and batch types, are operated under reduced pressure or pressurized conditions for aspirating slurry suspensions or discharging filtrate. In addition, it is necessary to provide a powder transfer device for transferring solids after solid-liquid separation to a next vessel. Thus, there are problems of complicated steps and an increased burden of construction cost in a method comprising filtering slurry suspensions in a vessel using a filtering device outside the vessel, and then transferring the filtered slurry suspensions to another vessel for reslurrying, dissolving or dispersing solids.